The present invention generally relates to integrated passive devices (IPDs). More specifically, the present invention relates to IPDs that have two or more passive ceramics-based components.
The continuing drive for component count reduction and miniaturisation has led in recent years to integration of inductors or capacitors with resistors into single surface mount devices. However, various technical problems have prevented successful integration of a component with a varistor, and there has been particular difficulty with integration of a capacitor with a varistor. The approaches to date have involved use of barrier materials between the components, adding expense and preventing miniaturisation to the extent desired.
Integration of a varistor and a capacitor is described in U.S. Pat. No. 5,870,273. However, this structure has a high resistivity layer separating the devices and thus has a complex structure. Also, the production technique involves dry-stacking application of layers using tapes. Thus, there is little flexibility in the production process, and material cost is high.
The invention is thus directed towards providing an improved varistor/capacitor IPD and method of production.
According to the present invention, there is provided an integrated passive device that includes a varistor and a capacitor. The varistor and the capacitor each have a ceramic oxide dielectric and inner electrodes having similar thermal expansion and shrinkage characteristics, and there is no barrier layer between the varistor and the capacitor.
In one embodiment, the varistor dielectric is of ZnO material.
In another embodiment, the capacitor dielectric comprises bismuth and niobate-based oxides.
In a further embodiment, the capacitor dielectric further comprises magnesium-based oxides.
In one embodiment, the capacitor dielectric material has a pyrochlore structure.
In another embodiment, the varistor dielectric particle size is approximately 1.5 xcexcm and the capacitor dielectric size is approximately 3.0 xcexcm.
In one embodiment, each of the capacitor and the varistor comprises a plurality of layers of dielectric and inner electrodes.
In another embodiment, the capacitor electrodes and the varistor electrodes are of platinum material.
In a further embodiment, the device includes feed-through end terminations and external capacitor and varistor terminations.
According to another aspect of the present invention the invention provides a process of producing an integrated passive device. The method includes the steps of applying wet layers of the capacitor dielectric, the capacitor inner electrode, the varistor dielectric, and the varistor inner electrode materials; and sintering the layers to provide the integrated passive device.
In an embodiment, the varistor dielectric particle size is approximately 1.5 xcexcm and the capacitor particle size is approximately 3.0 xcexcm.
In another embodiment, the capacitor dielectric material is prepared by milling powder with deionized water to provide a slurry; drying the slurry to provide dried powder; calcinating the dried powder for six hours at approximately 800xc2x0 C.; and adding solvent binders.
Additional features and advantages will be described in, and apparent from, the following Detailed Description of the Presently Preferred Embodiments and the Drawings.